在不加入实体到Linq的情况下获取外键值[关闭]

Question

Employee 表具有与Department 表的Id 列相关的Departmentid 外键。

现在，如果我从Employee 表中选择所有行，我应该在Employee 表的外键列中获取它们各自DepartmentId 的部门名称。

我正在使用实体框架，我可以通过创建Department 表的另一个对象来使用连接。

输出应该是这样的：

EmployeeName    EmployeeAddress  EmployeeDepartment
    abc            xyz                  IT

它应该自动获取Employee的外键值

lamiEntities1 lam = new lamiEntities1();
        var query =( from sls in lam.sales.AsEnumerable() join it in lam.items on sls.ItemId equals it.Id orderby sls.Id descending
                    select new

                    {
                        ItemName = it.ItemName,
                        TotalAmounts = sls.Amount,
                        Remarks=sls.Remarks,
                        Dates = sls.Date

                    }).Take(20);

        GridView1.DataSource = query;
        GridView1.DataBind();

在这里我如何删除加入并使用 itemid 外键直接使用 itemname

Answer 1

我猜这就是你要找的东西：

你可以制作一个 DTO(Data Transfer Object)，在层之间传输数据

public class EmployeeWithDepartmentDto
{
    public string EmployeeName { get; set; }
    public string EmployeeAddress { get; set; }
    public string DepartmentName { get; set; }
}

你会得到这样的结果：

var result = employeeRepository.Select(e => new EmployeeWithDepartmentDto { EmployeeName = e.Name, EmployeeAddress = e.Address, DepartmentName = e.Department.Name });

foreach (var employeeWithDepartmentDto in result)
     Console.WriteLine($"Name: {employeeWithDepartmentDto.EmployeeName}, Address: {employeeWithDepartmentDto.EmployeeAddress}, Department: {employeeWithDepartmentDto.DepartmentName}");

Here is an example in DotNetFiddle

如果不想创建 DTO 类，可以使用匿名对象进行查询

var result = employeeRepository.Select(e => new { EmployeeName = e.Name, EmployeeAddress = e.Address, DepartmentName = e.Department.Name });

或者你可以这样查询，使用 Linq-To-Sql：

var result = from e in employeeRepository
                select new EmployeeWithDepartmentDto
                {
                    EmployeeName = e.Name,
                    EmployeeAddress = e.Address,
                    DepartmentName = e.Department.Name
                }

如果您将 EF 与 Eager Loading 一起使用，则必须使用 Include，这样：

lamiEntities1 lam = new lamiEntities1();
    var query =( from sls in lam.sales.Include("item")
                orderby sls.Id descending
                select new

                {
                    ItemName = sls.Item.ItemName,
                    TotalAmounts = sls.Amount,
                    Remarks=sls.Remarks,
                    Dates = sls.Date

                }).Take(20);